The present disclosure relates to optical devices that include light emitting diodes (LEDs). In particular, the disclosure relates to miniaturized reflectometers which may be used, for example, in an implantable medical device (IMD).
Implantable medical devices, such as implantable pacemakers and implantable cardioversion defibrillators, monitor cardiac activity to detect various types of cardiac arrhythmias and to provide appropriate therapy based upon the type of arrhythmia detected. Cardiac arrhythmia detection is generally based upon an analysis of one or more electrical and hemodynamic functions of the heart.
ICDs are used to deliver high-energy cardioversion or defibrillation shocks to a patient's heart when atrial or ventricular fibrillation is detected. Cardioversion shocks are typically delivered in synchrony with a detected R-wave when fibrillation detection criteria are met. Defibrillation shocks are typically delivered when fibrillation criteria are met, but the R-wave cannot be discerned from signals sensed by the ICD.
Delivery of a cardioversion or defibrillation shock can be painful to the patient, and consumes energy from the battery of the ICD. It is desirable, therefore, that shocks be delivered only when they are necessary.
Sensing of additional physiologic parameters may be useful in enhancing arrhythmia detection and a determination of appropriate therapy, as well as for other physiologic monitoring and therapy applications. Among the sensors proposed for use with implantable medical detectors are optical hemodynamic sensors and tissue perfusion sensors. These optical sensors include one or more light sources (such as light-emitting diodes) and a photodetector, such as a photodiode. Multiple wavelengths of light may be emitted by the light-emitting diodes, and the amount of reflected light at each wavelength can be detected and processed to generate an output signal for use by the implantable medical device as part of its arrhythmia detection analysis, physiologic monitoring, or other therapy applications.